In fabricating a semiconductor integrated circuit device a fine pattern is transferred on a semiconductor wafer by lithography. In lithography a projection exposure apparatus is typically used and a pattern of a photomask attached on the apparatus is transferred onto the semiconductor wafer to form a pattern of a device.
In recent years there has been a demand for highly integrated devices and the devices' increased speed of operation and in order to meet the demand finer patterns are pursued. Under such circumstance, exposure apparatuses have conventionally been used with a numerical aperture (NA) increased to provide increased resolution.
Furthermore, as a method improving an effective NA a method of exposure referred to as immersion lithography has also been considered. In immersion lithography exposure, a space between a lens and a plane of photoresist serving as a sample to be printed is filled with liquid to increase the space's index of refraction to provide improved effective NA. (As seen from a different point of view, exposure is done with light having a reduced effective wavelength.) A technique associated with immersion lithography is described for example in non-patent Document 1 indicated hereinafter.
Thus there is an increasing demand for increased effective numerical aperture to provide patterns improved in contrast (or resolution). Currently, an apparatus with an NA of 0.9 or higher has been produced as a prototype. Furthermore, an exposure apparatus has also been planed that is combined with immersion lithography to provide an NA as converted of approximately 1.3. It is known that when such an extremely high numerical aperture exposure apparatus is used a pattern transferred significantly varies in contrast depending on the direction of polarization of light employed for exposure.
In general it is known that when polarized light along a direction in which a pattern extends (hereinafter also referred to as S polarized light) is used to provide exposure, a high contrast is obtained. When non-polarized light is used to provide exposure, resolution is reduced. When polarized light perpendicular to the direction in which the pattern extends (hereinafter also referred to as P polarized light) is used to provide exposure, further decreased resolution is provided. This is described for example in Japanese Patent Laying-Open Nos. 6-275493 (Conventional Example 1), 5-90128 (Conventional Example 2), and 6-140306 (Conventional Example 3).
Patent Document 1: Japanese Patent Laying-Open No. 6-275493
Patent Document 2: Japanese Patent Laying-Open No. 5-90128
Patent Document 3: Japanese Patent Laying-Open No. 6-140306
Non-Patent Document 1: “Immersion Lithography Technology”, NIKON corp. [made available on Feb. 19, 2004].